MEMS beam steering and fisheye receiving lens for LiDAR system

ABSTRACT

The present disclosure describes a system and method for a binocular LiDAR system. The system includes a light source, a beam steering apparatus, a receiving lens, a light detector. The light source is configured to transmit a pulse of light. The beam steering apparatus is configured to steer the pulse of light in at least one of vertical and horizontal directions along an optical path. The lens is configured to direct the collected scattered light to the light detector. The electrical processing and computing device is electrically coupled to light source and the light detector. The light detector is configured to minimize the background noise. The distance to the object is based on a time difference between transmitting the light pulse and detecting scattered light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/857,566, filed Dec. 28, 2017, which claimspriority to U.S. Provisional Patent Application No. 62/442,728, entitled“MEMS BEAM STEERING AND FISHEYE RECEIVING LENS FOR LiDAR SYSTEM”, filedon Jan. 5, 2017, the contents of each of which are hereby incorporatedby reference in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to a light detection andranging (LiDAR) system and, more specifically, to systems and methodsfor steering consecutive light pulses to illuminate objects in a fieldof view and binocularly collecting the scattered light from each lightpulse for ranging the objects in the field of view.

BACKGROUND OF THE DISCLOSURE

A LiDAR system can be used to measure the distance between an object andthe system. Specifically, the system can transmit a signal (e.g., usinga light source), record a returned signal (e.g., using light detectors),and determine the distance by calculating the delay between the returnedsignal and the transmitted signal.

SUMMARY OF THE DISCLOSURE

The following presents a simplified summary of one or more examples inorder to provide a basic understanding of the disclosure. This summaryis not an extensive overview of all contemplated examples, and is notintended to either identify key or critical elements of all examples ordelineate the scope of any or all examples. Its purpose is to presentsome concepts of one or more examples in a simplified form as a preludeto the more detailed description that is presented below.

In accordance with some embodiments, a method for light detection andranging (LiDAR) scanning detection is provided. The method includestransmitting a pulse of light from a light source; steering the pulse oflight at an object along an optical path; collecting scattered lightfrom the pulse of light dispersed from the object; converging thescattered light onto a light detector; and determining a distance to theobject based on a time difference between transmitting the light pulseand detecting the scattered light. While the description below uses avehicle as an example, the centralized laser delivery system andmultiple LiDARs can be disposed in or integrated with robots, multiplelocations of a building for security monitoring purposes, orintersections or certain location of roads for traffic monitoring, andso on.

In accordance with some embodiments, a light detection and ranging(LiDAR) scanning system is provided. The system includes: a light sourceconfigured to transmit a light pulse; a beam steering apparatusconfigured to steer the light pulse in at least one of vertical andhorizontal directions along an optical path; a light convergingapparatus configured to direct the collected scattered light to a focalplane; a light detector disposed at or in proximity to the focal plane,wherein the light detector comprises a plurality of detector segments;and an electrical processing and computing device. The electricalprocessing and computing device is configured to: based on the steeringof the light pulse, select a subset of the plurality of detectorsegments; deactivate a particular detector segment of the plurality ofdetector segments, wherein the particular detector segment is not partof the subset of the plurality of detector segments; and detect, usingthe selected subset of the plurality of detector segments, a scatteredlight generated based on the light pulse illuminating an object in theoptical path.

In accordance with some embodiments, a computer-implemented method foroperating a light detection and ranging (LiDAR) system, which includes alight source, a beam steering apparatus, and a light detector having afirst detector segment and a second detector segment, comprises:transmitting, with the light source, a light pulse; steering, with thebeam steering apparatus, the light pulse in at least one of vertical andhorizontal directions along an optical path; directing, with the lightconverging apparatus, the collected scattered light to a focal plane;based on the steering of the light pulse, selecting a subset of theplurality of detector segments; and detecting, using the selected subsetof the plurality of detector segments, a scattered light generated basedon the light pulse illuminating an object in the optical path.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described aspects, referenceshould be made to the description below, in conjunction with thefollowing figures in which like-referenced numerals refer tocorresponding parts throughout the figures.

FIG. 1 illustrates an exemplary binocular LiDAR system with receivingfisheye lens and filter, according to some embodiments of thedisclosure.

FIG. 2 illustrates an exemplary segmented detector and a received beamspot that moves through the detector's active areas, according to someembodiments of the disclosure.

FIG. 3 illustrates an exemplary solar spectrum of spectral irradianceversus wavelength.

FIG. 4 illustrates an exemplary plot of extinction coefficients versuswavelength in air with and without aerosols.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well-known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Examples of LiDAR systems and processes will now be presented withreference to various elements of apparatuses and methods. Theseapparatuses and methods will be described in the following detaileddescription and illustrated in the accompanying drawing by variousblocks, components, circuits, steps, processes, algorithms, etc.(collectively referred to as “elements”). These elements may beimplemented using electronic hardware, computer software, or anycombination thereof. Whether such elements are implemented as hardwareor software depends upon the particular application and designconstraints imposed on the overall system.

In the following description of examples, reference is made to theaccompanying drawings which form a part hereof, and in which it is shownby way of illustration specific examples that can be practiced. It is tobe understood that other examples can be used and structural changes canbe made without departing from the scope of the disclosed examples.

Although the following description uses terms “first,” “second,” etc. todescribe various elements, these elements should not be limited by theterms. These terms are only used to distinguish one element fromanother. For example, a first pulse signal could be termed a secondpulse signal, and, similarly, a second pulse signal could be termed afirst pulse signal, without departing from the scope of the variousdescribed embodiments. The first pulse signal and the second pulsesignals are both pulse signals, but they may not be the same pulsesignal.

The terminology used in the description of the various describedembodiments herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used in thedescription of the various described embodiments and the appendedclaims, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

The term “if” is, optionally, construed to mean “when” or “upon” or “inresponse to determining” or “in response to detecting,” depending on thecontext. Similarly, the phrase “if it is determined” or “if [a statedcondition or event] is detected” is, optionally, construed to mean “upondetermining” or “in response to determining” or “upon detecting [thestated condition or event]” or “in response to detecting [the statedcondition or event],” depending on the context.

In order to reduce the size of LiDAR systems, usingmicro-electro-mechanical systems (MEMS) to project a laser beam is adesirable choice. Such on-chip solutions reduce the size of the LiDARsystem. However, these on-chip MEMS designs yield an optical aperturecross-section that is a few (e.g., less than 5) millimeters or less in acoaxial receiving scheme, which limits the visibility of the LiDARsystem. It has been found that a larger optical aperture cross-sectionboosts the collection efficiency of scattered light. A collection lenswith wide acceptance angle, e.g., a fisheye lens, and a large area photodetector with fast speed and high sensitivity is needed to avoidmechanically tuning optics in a receiving path. However, this will alsoincrease the amount of background light, and thus noise, entering thereceiving system. As such, it is desired to increase the cross-sectioncollection optical aperture of a LiDAR system while lowering thebackground noise floor.

The present disclosure describes a binocular MEMS steering system forLiDAR. The LiDAR system can include a laser source that emits ortransmits laser light (e.g., laser pulses), a beam steering apparatus, alight converging apparatus, a light detector, and/or an electricalprocessing and computing device (e.g., a microprocessor). As discussedbelow, these components of the LiDAR system may be configured to operatewith MEMS designs in an optimal way.

As discussed above, while a larger optical aperture cross-section booststhe collection efficiency of scattered light, the larger cross-sectionalso increases the amount of background light, and thus noise, enteringthe receiving system. Reducing the amount of background light can beaccomplished by selecting wavelength of the laser source and/or using amatched narrow band filter. Specifically, the wavelength of the lasersource can be configured such that it falls into a band of atmospherewindows. FIG. 3 illustrates an exemplary solar spectrum of spectralirradiance versus wavelength, and FIG. 4 illustrates an exemplary plotof extinction coefficients versus wavelength in air with and withoutaerosols (e.g., fog). As an example, FIG. 3 shows that at 1.38 μmwavelength, the radiation at sea level is minimal. Similarly, FIG. 4shows that at that wavelength, the extinction coefficient is relativelyhigh. Thus, at this wavelength, there is minimal background light, andthus noise, from sun light in atmosphere near sea level. Thus, a 1.38 μmwavelength of a vapor absorption line can be selected as laser workingwavelength in this case.

Additionally or alternatively, a matched narrow band filter can bedisposed in the receiving beam path to reduce the collection of lightsthat are not of the desirable wavelength(s). The matched narrow bandfilter can be an optical filter that rejects or substantially reducesbackground light. For example, the optical filter can be a bandpassfilter such as a Lyot filter, a Fabry-Perot interferometer, or any othertunable filters.

In some embodiments, the MEMS beam steering apparatus can include a MEMSdevice that uses micro-mirrors. The MEMS mirror can steer the laserlight generated by the laser source in two or three dimensions toilluminate objects in a field of view. It is appreciated that the MEMSbeam steering apparatus can also include other MEMS components such asoptical switches, optical cross-connects, lens, etc.

To enhance the visibility of the LiDAR system, the exemplary LiDARsystem can further include a MEMS beam steering apparatus coupled with afisheye wide angle receiving lens. In some embodiments, the fisheye wideangle receiving lens can be configured to collect scattered lightgenerated from the pulses of light scattered at the objects. A fisheyelens can be a wide-angle lens that produces visual distortion intendedto create a wide panoramic or hemispherical image. Thus, the fisheyelens can collect scattered light within a wide-angle, thereby enhancingor increasing the visibility of the LiDAR system. A fisheye lens can be,for example, a circular fisheye lens or a full-frame fisheye lens. Insome embodiments, the fisheye lens's field of view can be selected orconfigured to match the field of view of the MEMS beam steering range.The fisheye wide angle receiving lens can be coupled to the MEMS beamsteering apparatus, for example, side by side.

In some embodiments, the exemplary LiDAR system can also include a lightdetector to detect the light collected by the fisheye lens (andoptionally filtered by the optical filter). In some instances, thedetector's size can be quite significant comparing to the size of thebeam spot. For example, the beam spot of a scattered light may besmaller than 100 micrometers, while the detector can have a size of afew millimeters in each dimension to cover the wide angle of field ofview. In other words, the fisheye lens system can operate in a fairlyunder-fill scenario, in which the beam size of the received beam spot ismuch smaller compared with total detector active area. This maysignificantly increase detector noise and reduce signal-to-noise ratio.A large area of the detector may also introduce a large junctioncapacitance, which is proportional to the area of the detector. Thelarge junction capacitance may slow down the amplifier and contribute toexcess noise gain of a following transimpedance amplifier. Furthermore,the extra unilluminated area in the detector contributes nothing tosignal but receiving a large amount of background noise, thus increasingcomputational burden.

FIG. 2 illustrates an exemplary segmented detector and a received beamspot that moves through the detector's active areas, according to someexamples of the disclosure. As depicted, a light detector having a largeactive area can be divided into small segments (e.g., divided into a 2×3or 2×4 array or other number of configurations of detector segments). Itis appreciated that the light detector can be divided into any number ofdetector segments for balancing or optimizing the overall systemperformance. In some embodiments, each segment can have smaller junctioncapacitance and can be coupled to its dedicated trans-impedanceamplifier.

Each detector segment can be illuminated by a beam spot (e.g., receivedscattered light) corresponding to the beam steering angle or position ofthe MEMS beam steering apparatus. From the steering MEMS, a skilledartisan can determine which detector segment is to be illuminated andLiDAR system can be focused on that segment of detector. For example, askilled artisan can select the detector segment based on registrationinformation from a MEMS steering mirror of the beam steering apparatus(e.g., position or pointing of the mirror). The extra cost of thissolution is some extra TIA amplifier which may increase system costslightly. In some examples, as shown in FIG. 1 , the exemplary LiDARsystem can further include a controller (e.g., one or more electricalprocessing and computing devices and memories) configured to coordinatebetween the MEMS beam steering apparatus and the activation of thedetector elements such that only certain detector elements (e.g., asingle detector element) are activated to receive the beam spot (e.g.,scattered light from an object) corresponding to the steering angle orposition of the MEMS steering apparatus. As illustrated in FIG. 2 , forexample, in the 2×4 detector array, some detector elements can beactivated while the other detector elements are deactivated or turnedoff. As a result, junction capacitance of a detector can besignificantly reduced and in turn, the signal-to-noise ratio can beimproved. In some embodiments, the light detector can be implementedusing an InGaAs-based detector (or array of detectors) and/or aSiGe-based detector.

In some examples, after determining which detector segment(s) are to beilluminated, the LiDAR system turns off (e.g., powers off) the rest ofthe detector segments on the detector array to save power and improvethermal management of the system if it is necessary (e.g., if theoverall power consumption of the system exceeds a predeterminedthreshold). In some examples, the LiDAR system does not turn off therest of the detector segments and allows all of the detector elements todetect collected scattered light. However, the system can forgoprocessing the signals detected by the rest of the detector segments,thus reducing computational burden.

In some embodiments, an exemplary LiDAR system can further include asecond detector configured to provide auto-balancing. For example, thesecond detector can have the same type or configuration as the firstdetector that detects the received scattered light generated by anobject within the LiDAR's detection range (e.g., the detector describedabove). The second detector, however, can be configured to receive onlybackground light or noise and provide the noise signal to thecontroller. In some examples, the system performs auto-balancing byautomatically adjusting the ratio between the output caused bybackground light received by the first detector and the output caused bybackground light received by the second detector to be one or close toone. The controller can thus correlate the signals provided by the firstand second detectors by, for example, subtracting the background noisesignals provided by the second detector from the signal provided by thefirst detector (which includes both the scattered light generated by anobject and the background noise). The auto-balancing can enhance theperformance of the LiDAR system under certain conditions where thebackground noise may not be readily distinguished from the scatteredlight of an object. For example, during night time, many ambient lightsare illuminating and thus background noise may include light at thelaser wavelength used by the LiDAR system. As a result, absent ofauto-balancing, the scattered light from an object may not be readilydistinguished from ambient lights.

It should be appreciated that the receiving part of the exemplary LIDARsystem described herein can have no moving parts. In other examples,moving parts may be included.

What is claimed is:
 1. A light detection and ranging (LiDAR) scanningsystem, comprising: a light detector disposed at or in proximity to afocal plane of scattered light, wherein the light detector comprises aplurality of detector segments and the scattered light is generatedbased on a light pulse illuminating an object; and an electricalprocessing and computing device configured to: obtain a subset of theplurality of detector segments; deactivate a particular detector segmentof the plurality of detector segments, wherein the particular detectorsegment is not part of the subset of the plurality of detector segments;and detect, using the subset of the plurality of detector segments, thescattered light.
 2. The LiDAR scanning system of claim 1, wherein theelectrical processing and computing device is further configured todetermine a distance to the object based on the scattered light detectedby the subset of the plurality of detector segments.
 3. The LiDARscanning system of claim 2, wherein deactivating the particular detectorsegment comprises: powering off the particular detector segment.
 4. TheLiDAR scanning system of claim 2, wherein deactivating the particulardetector segment comprises: detecting, using the particular detectorsegment, a second scattered light; and forgoing determining a distanceto the object based on the second scattered light detected by theparticular detector segment.
 5. The LiDAR scanning system of claim 1,wherein a light source generating the light pulse is a laser lightsource.
 6. The LiDAR scanning system of claim 1, wherein the light pulsecomprises a signal of a predetermined wavelength range.
 7. The LiDARscanning system of claim 6, wherein the predetermined wavelength rangefalls into a band of an atmosphere window.
 8. The LiDAR scanning systemof claim 6, further comprising an optical filter configured to filterpulse signals outside the predetermined wavelength range.
 9. The LiDARscanning system of claim 1, further comprising a light convergingapparatus directing the scattered light to the focal plane andcomprising a wide angle receiving lens.
 10. The LiDAR scanning system ofclaim 1, wherein the light detector is a first light detector, andwherein the LiDAR scanning system comprises a second light detectorconfigured to receive background light.
 11. The LiDAR scanning system ofclaim 10, wherein the electrical processing and computing device isconfigured to reduce noise in a light signal received by the first lightdetector based on the background light received by the second lightdetector.
 12. The LiDAR scanning system of claim 11, wherein reducingnoise in the light signal received by the first light detector comprisesadjusting a ratio between an output caused by background light receivedby the first light detector and an output caused by the background lightreceived by the second light detector.
 13. The LiDAR scanning system ofclaim 1, further comprising a light converging apparatus directing thescattered light to the focal plane, wherein the light convergingapparatus is a 2D or 3D MEMS device.
 14. The LiDAR scanning system ofclaim 1, further comprising a beam steering apparatus configured tosteer the light pulse, wherein the beam steering apparatus comprises oneor more micro-mirrors.
 15. The LiDAR scanning system of claim 1, furthercomprising a light converging apparatus directing the scattered light tothe focal plane, wherein the light converging apparatus comprises afisheye lens.
 16. A computer-implemented method for operating a lightdetection and ranging (LiDAR) system, the LiDAR system comprising alight detector comprising a plurality of detector segments, wherein thelight detector is disposed at or in proximity to a focal plane ofscattered light and the scattered light is generated based on a lightpulse illuminating an object, the method comprising: obtaining a subsetof the plurality of detector segments; deactivating a particulardetector segment of the plurality of detector segments, wherein theparticular detector segment is not part of the subset of the pluralityof detector segments; and detecting, using the subset of the pluralityof detector segments, the scattered light.
 17. The computer-implementedmethod of claim 16, further comprising determining a distance to theobject based on the scattered light detected by the subset of theplurality of detector segments.
 18. The computer-implemented method ofclaim 17, wherein deactivating the particular detector segmentcomprises: powering off the particular detector segment.
 19. Thecomputer-implemented method of claim 17, wherein deactivating theparticular detector segment comprises: detecting, using the particulardetector segment, a second scattered light; and forgoing determining adistance to the object based on the second scattered light detected bythe particular detector segment.
 20. The computer-implemented method ofclaim 16, wherein the light detector is a first light detector, andwherein the LiDAR system comprises a second light detector configured toreceive background light, and the method further comprises reducingnoise in a light signal received by the first light detector based onthe background light received by the second light detector.